64 THE CARBOHYDRATE ECONOMY OF CACTI. 



In none of the leaves employed by Czapek did starch formation occur at 

 low temperatures with sugar concentrations under 7 per cent, while at 

 ordinary temperatures a 1 per cent saccharose solution produced starch in 

 abundance. 



All of these results indicate that the enzymatic equilibria are so adjusted 

 that at high temperatures there takes place a general reversion of the carbo- 

 hydrates to the polysaccharides, while at lower temperatures there is general 

 inversion to the simpler sugars. 



VIII. AEROBIC AND ANAEROBIC RESPIRATION. 



Kichards 1 made a number of determinations of the CO 2 emission and the 

 CO 2 /O 2 ratio of Opuntia versicolor in atmospheres of hydrogen and of 

 nitrogen. The most noteworthy result of these experiments is the relatively 

 high rate of carbon-dioxid emission despite the absence of oxygen. The 

 amount of carbon dioxid produced in normal air at 21 was about twice that 

 emitted in the absence of oxygen, while at 30 the amounts were almost 

 equal. Thus the CO 2 per gram-hour at 21 was in air 0.24 and 0.25 mg., 

 in nitrogen 0.17 and 0.15 mg., while at 35 it was in air 0.30 and 0.33 mg., 

 and in nitrogen 0.38 mg. The acidity as determined by titration does not 

 diminish at the rate at which it does in the presence of oxygen. It appears, 

 therefore, that the carbon dioxid which is produced does not arise from the 

 breaking down of the organic acids to the same extent as in the normal 

 cases. Some knowledge of the role of the carbohydrates under anaerobic 

 conditions seemed, therefore, highly desirable. 



Joints of Opuntia phwacantha were selected in the manner previously 

 described. One set of joints was analyzed immediately, another set was 

 placed under a large bell-jar provided with tubes for circulation of air in a 

 dark room kept at 20, and a third set was placed in the same dark room 

 under a bell- jar in an atmosphere free of oxygen. 



Anaerobic conditions were produced by the employment of the methods 

 of Ruzieka. 8 The bell-jar (15 liters capacity) was placed in a shallow pan 

 containing 500 c. c. of a 1 per cent aqueous phenol solution, 70 c. c. 20 per 

 cent aqueous Na 2 CO 3 solution and 50 grams dextrose to which was added 

 about 500 c. c. of paraffin oil. This mixture served as a seal. In this pan 

 stood a large glass triangle on which was placed a shallow glass dish con- 

 taining a quantitiy of pyrogallol and a stick of KOH. In this dish stood 

 another glass triangle which supported a container made of wire screen in 

 which had been placed the cactus joints. In the pyrogallol dish there was 

 also placed a small beaker containing an indicator solution made of 50 c. c. 

 1 per cent phenol solution, 5 c. c. 20 per cent Na 2 CO 3 and 1 g. c. p. dex- 

 trose, to which was added 0.5 c. c. prepared sulphuric acid indigo solu- 

 tion. The oxygen was removed from the bell-jar by burning a small jet of 



1 RICHABDS, H. M. L. c., pp. 57, 84. 



2 ABDEBHALDEN, E. Handbuch der Biochem. Arbeitsmethoden. Vol. Ill (2), 1239, 



1910. 



